1. Field of the Invention
The present invention relates to a pigment ink, an ink-jet recording process, a recording unit, an ink cartridge and an ink-jet recording apparatus.
2. Related Background Art
With the spread of ink-jet recording systems, it has become a priority to improve the quality and fastness properties of prints. With respect to fastness properties of prints, for example, water fastness, Japanese Patent Application Laid-Open No. 4-226175 and U.S. Pat. No. 5,053,495 disclose novel black dyes and inks which can provide images having good water fastness.
Black inks using a pigment have been reported to form black images excellent in print quality and fastness properties such as water fastness and light fastness on plain paper.
For example, Japanese Patent Application Laid-Open No. 5-179183 discloses a pigment ink stabilized with a block copolymer of the AB or BAB type. Japanese Patent Application Laid-Open No. 6-136311 discloses a pigment ink which comprises a block copolymer composed of a hydrophobic polymer having a basic amine functional group and a hydrophilic polymer having nonionic and acidic functional groups, which can provide prints of excellent quality and has excellent dispersion stability. Japanese Patent Application Laid-Open No. 7-53841 has proposed a pigment ink for ink-jet, which comprises a triblock copolymer of the ABC type, has excellent dispersion stability and can provide prints of excellent quality.
On the other hand, pigment inks using, as a coloring material, the so-called self-dispersing type carbon black, which does not require the addition of any dispersing agent to the inks, have been proposed with a view toward improving the ejection stability thereof upon ink-jet recording. For example, U.S. Pat. Nos. 5,554,739 and 5,571,311 disclose a production process of self-dispersing type carbon black to the surface of which at least one hydrophilic group is bonded directly or through another atomic group. A pigment ink comprising such self-dispersing type carbon black can provide prints of excellent quality and has excellent dispersion stability without using any block copolymer.